The invention relates to a drive device for a heat sensitive recording head used in a facsimile printer or the like.
In a prior heat sensitive recording head of this general type intended for line scanning, the drive leads correspond to the recording positions in the ratio of 1:1, that is, one drive head is provided for each recording position. However, such a heat sensitive recording head is disadvantageous in that, where recording must be carried out with high recording density so as to obtain a high quality, the distance between the leads is necessarily short and, accordingly, it is difficult to connect the leads to the drive circuit.
In order to overcome this difficulty, a recording head as shown in FIG. 1 has been proposed. In this head, leads b are disposed along both sides of a substrate a and heat generating elements c are provided between the ends of the leads b so that the lead spacing on each side is twice the spacing between heat generating elements c. However, this recording head is disadvantageous in that the recording positions do not correspond directly to the leads b and, accordingly, the recording head cannot be driven by a conventional drive circuit.
In order to eliminate these drawbacks, a drive circuit as shown in FIGS. 2A-2D has been proposed. In this drive circuit, data signals to be recorded are divided into two groups, namely, an odd-number group and an even-number group according to the recording position arrangement and the data signals of each of the groups are further divided into plural groups and the heat generating elements c are driven by the data signals thus processed. However, this drive technique is still disadvantageous in that, as four separate structures are required as illustrated by FIGS. 2A-2D, the recording speed is relatively slow.
A drive device as shown in FIGS. 3A and 3B has been known, which was intended for eliminating the above-described difficulty. In that drive device, data signals to be recorded are distributed to every other element according to the recording position arrangement with two such groups of data signals provided to drive the heat generating elements c. With this drive technique, the driving time is reduced to a half of that in the case of FIGS. 2A-2D, that is, the driving speed is doubled.
In general, a heat sensitive recording head employed in facsimile is rather long. Thus, a typical practical recording head is formed by plural blocks divided into two groups with one line of a picture provided by repeatedly driving the heat sensitive elements with the drive circuit. In the case, if the same energy is supplied to a first selected group of heat sensitive elements in one block and then to a second selected group, the second group is affected by residual heat from the first group as a result of which the coloring density becomes higher and the printing dot size becomes larger for the second group. That is, the formed picture is non-uniform in its entirety. Therefore, the heat sensitive recording head shown in FIG. 3 is employed with a technique in which the heat generating elements are driven by making the amount of electrical energy supplied to the first group different from that supplied to the second group so as to provide a uniform picture. However, it should be noted that the required drive circuit is intricate in construction and high in manufacturing cost.